I don't think anyone addressed what "shortwave" is. Here's a beginner primer.
The radio spectrum, from about 300Kc (or Khz) to 510Kc is considered Longwave. In the States, it was referred to as the "Marine Band". That is, the length of the waveform from the antenna, and the space between positive and negative pulses, get longer as the frequency goes down. It was used for many years for Marine Navigation and Beacons.
American commercial "AM" band, 530-1700Kc, is Medium Wave (as it is called exactly that in Europe). Older radios will call it "Standard Broadcast".
From 1710Kc (1.71Mc or MHz) to 26Mc (ish) is considered international "shortwave" because the wavelength is small. BUT, in these frequencies, some really cool stuff happens.
Just like you can pick up many AM stations from many states away at night (clear channels), shortwave uses the same physics to bounce signals from the ground (daytime radio reception - groundwave) to the ionishpere, then back down (Skywave). Skywave in the shortwave bands works both day AND night, depending on the frequency, or Meter Length. The Meter determines the length of the antenna needed to transmit efficiently.
And poor weather conditions will bring in distant signals even on a few watts, like the CB Band (27Mc). They usually call that "skip", as the signal bounces from earth to clouds/ionisphere back to your receiving antenna. Although some may point out (correctly) that many of the low watt CB stations have , well, "help".
How did I do oldtimers?
